Category: European XFEL

15 years of European XFEL

15 years of European XFEL

European XFEL, one of the world’s most powerful X-ray sources, is celebrating the 15th anniversary of the international treaty that laid the foundation for its creation this year. On 30 November 2009, ten European countries jointly decided to implement the ambitious research project and create an internationally accessible research facility that would offer new, unparalleled research opportunities to scientists from all over the world.

“European XFEL has become a symbol of successful scientific collaboration across national borders,” says Thomas Feurer, Managing Director and Chairman of the Management Board of European XFEL.

The X-ray laser, whose first light beam was generated in 2017, has since enabled ground-breaking research worldwide. Researchers from disciplines like physics, chemistry, biology, medicine and materials science benefit now from the facility at seven instruments, whose intense X-ray light beam offers unique insights into the molecular structure of matter and dynamic electronic or chemical processes in real time. Thanks to its high beam power, molecular structures and chemical reactions can be observed with unrivalled precision and speed, far exceeding conventional technologies. Most recently, researchers were able to show that the European XFEL can generate record-breaking X-ray pulses in the attosecond range with terawatt power.

The construction of the facility was supported by strong partnerships right from the start: the close collaboration with the Deutsches Elektronen-Synchrotron (DESY) in Hamburg played a decisive role in the realisation and operation of the European XFEL.

Read more on European XFEL website

Image: Ministers, state secretaries and other government representatives from ten partner countries met in November 2009 in the Hamburg City Hall to sign the international European XFEL agreement.

Credit: European XFEL

Squeeze it! High-power attosecond X-ray pulses at megahertz repetition rates

Squeeze it! High-power attosecond X-ray pulses at megahertz repetition rates

A research team at European XFEL and DESY has achieved a major advance in X-ray science by generating unprecedented high-power attosecond hard X-ray pulses at megahertz repetition rates. This advancement opens new frontiers in the study of ultrafast electron dynamics and enables non-destructive measurements at the atomic level.

Researchers have demonstrated single-spike hard X-ray pulses with pulse energies exceeding 100 microjoules and pulse durations of only a few hundred attoseconds. An attosecond is one quintillionth (10-18) of a second—a timescale that allows scientists to capture even the fastest electron movements in matter.

“These high-power attosecond X-ray pulses could open new avenues for studying matter at the atomic scale,” says Jiawei Yan, physicist at European XFEL and lead author of the study published in Nature Photonics. “With these unique X-rays, we can perform truly damage-free measurements of structural and electronic properties. This paves the way for advanced studies like attosecond crystallography, allowing us to observe electronic dynamics in real space.”

Traditional methods for generating such ultra-short hard X-ray pulses required dramatically reducing the electron bunch charge to tens of picocoulombs, which limited the pulse energy and practical use. The team developed a self-chirping method, utilizing the collective effects of electron beams and specialized beam transport systems at the European XFEL. This approach enables the generation of attosecond X-ray pulses at terawatt-scale peak power and megahertz repetition rates without reducing the electron bunch charge.

“By combining ultra-short pulses with megahertz repetition rates, we can now collect data much faster and observe processes that were previously hidden from view”, says Gianluca Geloni, group leader of the FEL physics group at the European XFEL. “This development promises to transform research across multiple scientific fields, especially for atomic-scale imaging of protein molecules and materials and investigating nonlinear X-ray phenomena.”

Read more on European XFEL website

Image: Scientists at European XFEL and DESY produce high-power attosecond X-ray pulses at megahertz repetition rates. With the help of special beam optics relativistic electrons (blue cloud) are strongly compressed (bright line in the centre). This leads to a very bright, high-power X-ray pulse on the attosecond timescale.

Credit: European XFEL; Illustration: Tobias Wüstefeld

European XFEL opens modern exhibition and conference centre

European XFEL opens modern exhibition and conference centre

Schenefeld, 20.11.2024 – Together with high-ranking guests, European XFEL today opens the modern Lighthouse exhibition and conference centre on its campus in Schenefeld near Hamburg to the public. The two-storey building offers space for a 350 m2 permanent exhibition, 200 m2 of special exhibition space, the Xcool Lab with two laboratories for students, and rooms for conferences and events. The name Lighthouse was suggested by the staff.

The new Lighthouse exhibition and conference centre of European XFEL offers a fascinating scientific experience. Together with the DESY visitor centre DESYUM, which is due to open in 2025, it will take visitors on an even more comprehensive journey of discovery into modern research with X-ray light sources and particle physics.

Guido Wendt, State Secretary for Science, Research and Culture, Schleswig-Holstein: “European XFEL enables cutting-edge international research, with outstanding experiments and brilliant results that inspire the global scientific community. We also want to communicate this to the public – and especially to schoolchildren. The new exhibition and conference centre with its two laboratories for schoolchildren will provide us with excellent support in the future.”

Eva Gümbel, State Councilor, Authority for Science, Research, Gender Equality and Districts of Hamburg: “At the European XFEL, researchers from all over the world carry out unique experiments and develop new research opportunities. With the new exhibition and conference centre, this can be experienced directly by students: through interactive exhibits, original pieces and multimedia presentations. The combination of excellent research and knowledge transfer is a real benefit for our science location and a great experience for all visitors.”

Schenefeld’s mayor Christiane Küchenhof: “Every lighthouse is unique, but the town of Schenefeld now has the most unique lighthouse in the world. The visitor and conference centre with this beautiful name will now share its light with many guests. I am delighted about this important new attraction on the Schenefeld science campus.”

Read more on European XFEL website

Image: The cutting of the red ribbon marks the official opening of the Lighthouse exhibition and conference centre (from left to right: Nicole Elleuche, Helmut Dosch, Eva Gümbel, Volkmar Dietz, Christiane Küchenhof, Guido Wendt, Federico Boscherini, Thomas Feurer)

Credit: European XFEL / Axel Heimken

Thomas Feurer elected as future Chairman of LEAPS

Thomas Feurer elected as future Chairman of LEAPS

At their annual meeting, the 16-member organisations of the League of European Accelerator-based Photon Sources (LEAPS) elected Prof. Dr Thomas Feurer, Chair of the Management Board of European XFEL, as their future chairman. LEAPS is a strategic initiative that brings together major European synchrotron radiation and free electron laser (FEL) facilities. Through joint efforts, LEAPS seeks to advance photon science and to maximize the impact of accelerator-based light sources in Europe. Feurer will succeed Jakub Szlachetko from the National Synchrotron Radiation Centre SOLARIS, Krakow (Poland). The handover will take place at the next plenary session in October or November next year. Until then, he will enjoy the status of Incoming Chair.

“It is quite an honour for me to serve as the next LEAPS chair”, says Thomas Feurer. “Alongside the 16 members, I will focus on strengthening the network, supporting successful EU applications, and advancing FEL-oriented initiatives. I am excited to turn our shared vision of leveraging our 16 research infrastructures to address societal challenges into a reality.”

Read more on XFEL website

Image: Thomas Feurer from European XFEL elected Chairman of LEAPS

Credit: European XFEL

Congratulations to the Nobel Prize winners in chemistry

Congratulations to the Nobel Prize winners in chemistry

The researchers at the world’s largest free-electron laser, the European XFEL, are delighted that Demis Hassabis, John M. Jumper and David Baker have been awarded the Nobel Prize in Chemistry. The decoding of protein structures is an important field of research for X-ray lasers such as the European XFEL.

David Baker has been an active user of the European XFEL since 2022. His team has actively participated in single-molecule imaging experiments at the Small Quantum Systems (SQS) and SPB/SFX instrument.

There, they recorded diffraction patterns of computationally designed proteins and single molecules for the first time.

“We are excited that David Baker has received the Nobel Prize for his ground-breaking work in the computer-aided design of de novo proteins”, says Thomas Feurer, Chairman of the Management Board of European XFEL. “We look forward to collaborating on upcoming experiments where he plans to explore the ultra-fast dynamics and behaviour of these innovative proteins with us.”

Read more on European XFEL website

Image: David Baker, Demis Hassabis and John Jumper. Ill. Niklas Elmehed

Credit: Nobel Prize Outreach

European XFEL creates exotic matter

European XFEL creates exotic matter

Exploring the extreme conditions reached in the interior of planets, including Earth, or during a fusion reaction, is a major challenge. By focusing the extremely powerful X-ray laser of European XFEL on a copper foil, researchers have created and investigated a state of matter very far from equilibrium, coined warm dense matter (WDM), that resembles such exotic environments. Their findings make remarkable strides in understanding and characterizing this elusive state of matter, which is crucial for advancing inertial confinement fusion, a process that holds promise for clean and abundant energy.

Heat can drastically change the state of matter: depending on the temperature, substances are solid, liquid or gaseous. In a certain temperature range, matter also assumes a state known as warm dense matter (WDM): it is too hot to be described by the physics of condensed matter, but at the same time too dense for the physics of weakly coupled plasmas. The boundary between warm dense matter and other states of matter is not precisely defined. Often a temperature range of 5,000 Kelvin to 100,000 Kelvin is specified at pressures of several hundred thousand bar, whereby one bar corresponds to the air pressure on Earth surface. WDM is not stable in our daily environment and is very difficult to produce or even examine in the laboratory. Typically, scientists compress samples in diamond anvil cells to reach high pressures, or use powerful optical lasers to turn solids into WDM for a tiny fraction of a second.

The intense X-ray pulses of European XFEL have now proved to be a very useful tool for generating and analysing warm dense matter. The researchers used copper as a sample material. “The high intensity of the pulses can excite the electrons in the copper foil to such an extent that it switches to the state of warm dense matter,” explains Laurent Mercadier, a scientist at the SCS[1] instrument who led the experiment: “This can be seen in a change in its light transmission.”

A metal that is irradiated by an intense X-ray pulse can become transparent if the electrons in the metal absorb X-ray energy so fast that there are no electrons left to excite. The remaining tail of the pulse can then penetrate the material unhindered. This is known as saturable absorption (SA). Conversely, a metal can become increasingly opaque if the front of the pulse creates excited states that have higher absorption coefficient than the cold metal. The tail of the pulse is then absorbed stronger, an effect known as reverse saturable absorption (RSA). Both processes are routinely used in optics, for example to generate a specific pulse length with lasers.

Read more on European XFEL website

Image: Laurent Mercadier checks the setup in the experimental chamber

Credit: European XFEL

Thomson scattering: Reaching unmatched level

Thomson scattering: Reaching unmatched level

Researchers at European XFEL have developed an innovative method to study warm dense matter with unprecedented accuracy. This kind of matter, that exists between condensed matter and plasma physics, can be found, for example, in astrophysical objects or is created during inertial confinement fusion. For the contributing scientists at the Center for Advanced Systems Understanding (CASUS), this advancement is a great aid to their mission of lifting the analysis of warm dense matter onto a solid foundation.

Studying astrophysical objects is a major challenge. Extreme conditions prevail there: high temperatures and immense densities. Here on Earth, the same applies to the investigation of inertial confinement fusion capsules during the implosion phase. At the High Energy Density (HED) instrument of European XFEL these conditions can be prepared there using the powerful drivers provided by the HiBEF consortium (Helmholtz International Beamline for Extreme Fields). Coupled with the brilliant X-ray flashes of the European XFEL, scientists can now study this exotic state of matter more closely than ever before.

Warm dense matter: an exceptional phenomenon

We normally think of matter here on Earth as existing in either a solid, liquid or gaseous state. Further afield in space, matter existing as a plasma can also be discovered, characterized as a hot and ionized gas. However, at high temperatures and immense densities, like that found in stars or when meteors crash onto planets, matter cannot be easily described as solid, or as a plasma and is instead named warm dense matter. Warm dense matter is too hot to be described by the physics of condensed matter and too dense for the physics of plasma. Typically, warm dense matter occurs at temperatures of 5,000 to several 100,000 Kelvin and pressures of several hundred thousand times greater than atmospheric pressure.

Discovery thanks to ultra-high-resolution X-ray Thomson scattering

A team led by Thomas Preston from the HED instrument at European XFEL has investigated the structure and properties of plasmons in ambient aluminum. Plasmons are collective oscillations of electrons and play a decisive role in the optical properties of metals, semiconductors, and in warm dense matter. An important method to investigate excitations in solids as well as warm dense matter is X-ray Thomson scattering. Here an X-ray photon is scattered in the material and loses energy and momentum in exciting a plasmon. With a spectrometer, scientists can identify these photons that have lost energy from the main beam of X-rays that are just scattered elastically.

Differently to previous work, which could only measure these excitations with X-rays with poor resolution on the order of a few electronvolts, Preston’s team and contributing scientists from Helmholtz-Zentrum Dresden-Rossendorf (HZDR) as well as the HZDR institute CASUS have now recorded ultra-high-resolution X-ray Thomson scattering spectra with an energy resolution improved more than tenfold meaning that they reached a resolution of less than one hundred millielectronvolt.

The team have published their findings recently in the journal Physical Review B, which honored the work with an “Editor’s Suggestion”. As the team reports, the new set-up enabled the investigation of the structure and properties of plasmons in aluminum in detail. “We realized that we could repurpose an existing setup that was designed to make even higher resolution measurements of vibrations in solids, which have energy losses much smaller than scattering from a plasmon, in fact only a few tens of millielectronvolts,” explains Preston. “Through a clever choice of our X-ray energy, we can instead measure energy losses up to 40 electronvolts with similar resolution. The accuracy of our measurements made it possible to eliminate long-standing discrepancies between simulations and experimental observations,” describes Preston. In future work, the team intend to use this method to benchmark simulations for plasmons at higher temperatures and compressions.

Read more on XFEL website

Image: The head of the HED instrument, Ulf Zastrau, assembling components in Interaction Chamber 1, where the experiments were carried out.

Credit: European XFEL

Frozen noble gas in the accelerator

Frozen noble gas in the accelerator

Researchers at European XFEL in Schenefeld near Hamburg have taken a closer look at the formation of the first crystallisation of nuclei in supercooled liquids. They found: The formation starts much later than previously assumed. The findings could help to better understand the creation of ice in clouds in the future and to describe some processes inside the Earth more precisely.

Every child knows that water freezes into ice when it gets icy cold. For water, this normally happens below zero degrees Celsius, the melting temperature of water. This is a fixed point on the Celsius temperature scale that we use.

However, the transition from the liquid to the solid phase is a very complex process and is difficult to study experimentally at the atomic level. One reason for this is that crystals are formed randomly: You don’t know exactly when and where it will happen. Furthermore, a liquid can remain in a metastable state for a long time: It remains liquid even though it should actually freeze and become solid. This makes it extraordinarily difficult to pinpoint the right moment for a crystal to form and watch its growth.

However, these effects are highly relevant in nature. For example, they play a decisive role in the formation of ice in clouds or in processes inside Earth.

Using the intense X-ray flashes of the European XFEL’s X-ray free-electron laser, an international team of researchers at the European XFEL in Schenefeld near Hamburg has now succeeded in precisely measuring the nucleation of supercooled liquids. The experiments took place in a vacuum so that the X-ray light does not interact with the molecules in the air, which would interfere with the experiments. Because of its complexity, however, water is one of the most difficult liquids to model. For that reason, the researchers used instead argon and krypton in liquid form in their experiments. In fact, supercooled noble-gas liquids are the only systems for which reliable theoretical predictions can be presently made.

The researchers explicitly investigated the so-called crystal nucleation rate J(T). This is a measure of the probability that a crystal will form in a certain volume within a certain time. The rate at which this happens is an important parameter, for example in order to be able to mathematically describe real processes in models – in weather forecasting, for example, or in climate models.

Read more on XFEL website

Image: X-ray of a crystal. The diffraction pattern results from 34,000 single-pulse x-ray exposures of a krypton jet shortly after the onset of crystal nucleation. The rings indicate x-ray scattering from specific molecular planes within the small crystals.

Credit: European XFEL

Preparing young engineers for cutting-edge science

Preparing young engineers for cutting-edge science

The MEDSI Early Career Engineering School 2024, held at European XFEL and DESY from 13 to 17 May, trained 80 young engineers and early career specialists in the design of state-of-the-art instrumentation for X-ray laser and synchrotron light sources.

Organised by European XFEL and DESY as part of the international MEDSI (Mechanical Engineering Design of Synchrotron Radiation Equipment and Instrumentation) conference series, the school focused on sharing knowledge to address the unique challenges of the technologies used in X-ray science facilities and instruments.

Participants learned about various technical aspects related to the mechanical design, construction and operation of synchrotron radiation facilities. The main objectives were to familiarise the participants with the main components of XFEL and synchrotron radiation sources, to introduce important design parameters and engineering tools, and to provide a basic understanding of X-ray optics and diagnostics.

In addition, experts from DESY, European XFEL and partner institutes presented new concepts and technologies for use in beamlines and experiments, and used practical examples to impart specialist knowledge for the design of key components.

With a focus on equipping young professionals with the necessary skills to meet future challenges, the MEDSI Early Career Engineering School 2024 served as a central platform for fostering expertise and innovation in synchrotron instrumentation design.

Read more on XFEL website

Image: The MEDSI Early Career Engineering School 2024

Finding the chink in corona’s armour

Finding the chink in corona’s armour

The COVID-19 pandemic resulted in millions of deaths. Despite an unparalleled collaborative research effort that led to effective vaccines and therapies being produced in record-breaking time, a complete understanding of the structure and lifecycle of the coronavirus known as SARS-CoV-2 is still lacking. Scientists used the biolabs and the SPB/SFX instrument at the European XFEL to study the main protease, or Mpro, of the virus to understand how it protects itself from oxidative damage. The results add key knowledge to our understanding of the workings of SARS-CoV-2 and the field of viral biology.

Between January 2020 and March 2023, over six million people died as a result of the respiratory disease COVID-19, and several hundred million were infected. The disease is caused by SARS-CoV-2, a coronavirus. “Coronaviruses are a group of RNA viruses that cause illnesses and diseases in mammals and birds”, explains European XFEL scientist Richard Bean. “However, despite their significant relevance for global human health, there is still a lot to learn about the structure and function of coronaviruses in general and SARS-CoV-2 in particular.”

In response to the outbreak of the pandemic, scientists and scientific organizations around the globe poured efforts into studying the structure, dynamics, and function of SARS-CoV-2 in search of vaccines and therapies. Due to its central role in the replication cycle of the virus, the main protease – an enzyme that liberates newly made pieces of the virus from one another – soon emerged as a key antiviral drug target. The main protease, or Mpro, is particularly attractive for drug development because it plays a central role in viral replication, and also because it is quite different from all human proteins. This allows therapies to specifically target the virus while minimizing side effects that might harm patients. Previous drug discovery programmes targeting other viruses have succeeded using viral protease inhibitors, making a successful outcome in the case of SARS-CoV-2 more likely. “While the height of the COVID-19 pandemic may have passed, there is still a lot of value in studying the SARS-CoV-2 virus”, enhances Thomas Lane from the Center for Free-Electron Laser Science (CFEL) in Hamburg. “COVID continues to present a significant health threat worldwide. Given the persistence of this virus and the possible emergence of future pathogenic coronaviruses, it is imperative we develop a deeper understanding of Mpro and its role in viral function.”

In a recent experiment at the SPB/SFX instrument at the European XFEL, Lane and colleagues used the intense X-ray beam to study Mpro. Several previous structural studies focusing on Mpro have highlighted a number of peculiarities. “Firstly, the protein forms a 3D structure known as a dimer when it is found in high concentrations”, explains European XFEL scientist Robin Schubert, who was involved in the experiment. “This structural habit seems to directly influence its activity—but we don’t know precisely why this is important for the virus.”

Read more on XFEL website

Image: An understanding of the structure and lifecycle of the SARS-CoV-2 virus is essential to develop vaccines and therapies.

Credit: CFEL

European XFEL elicits secrets from an important nanogel

European XFEL elicits secrets from an important nanogel

An international team led by Felix Lehmkühler from Deutsches Elektronen-Synchrotron DESY in Hamburg has investigated the temperature induced swelling and collapsing of the polymer poly-N-isopropylacrylamide (PNIPAm) at European XFEL at Schenefeld near Hamburg. Due to its dynamic changes, PNIPAm is used in medicine, e.g. for drug delivery, tissue engineering or sensorics.

PNIPAm is typically dissolved in water. Above a certain temperature, the so-called lower critical solution temperature (LCST), which is around 32 °C, it changes from a hydrophilic, water-loving state to a hydrophobic, water-repellent state. As consequence, nanogel particles, as investigated by Lehmkühler and co-workers, rapidly change their size above that temperature by expelling water.

This feature is useful for a variety of applications, including the controlled release of drugs in a patient’s body, as a model system for proteins and in tissue engineering, the cultivation of organic tissue for medical applications, or as bio-compatible temperature sensors. However, it was very difficult so far to watch these rapid phase transitions experimentally, and therefore to optimize them for different applications. Therefore, the precise characterisation of the kinetics of the changes of the PNIPAm polymer with temperature is still a lively research topic.

Read more on XFEL website

Image: Felix Lehmkühler at the instrument MID (Materials Imaging & Dynamics) of European XFEL where the experiments were done.

Credit: European XFEL

Röntgen medal for Robert Feidenhans’l

Röntgen medal for Robert Feidenhans’l

The Danish physicist Robert Feidenhans’l has spent almost his entire career working in the field of X-ray synchrotron radiation and free-electron lasers and is regarded as a pioneer in the use of X-rays from synchrotron radiation facilities. He is a co-founder of surface crystallography and was the first person to succeed in precisely determining surface structures experimentally. Feidenhans’l is an outstanding researcher who always regarded science as a means of promoting international understanding and collaboration.

His research includes nanophysics, in particular research into nanowires and the development of X-ray techniques for analysing materials. He was also instrumental in the development of X-ray imaging methods for the three-dimensional characterisation of materials and biological tissue, and was involved in high-resolution micro X-ray tomography in medicine, for example to investigate the interaction between bones and implants.

Between 2017 and 2023, Feidenhans’l was Chairman of the Management Board of the European X-ray laser and responsible for the transition from construction into full user operation. The international research facility in Schenefeld near Hamburg is one of the most powerful X-ray lasers in the world.

During his career, he has held numerous positions in science management. For example, he was Chairman of the Danish National Committee for Crystallography (1998-2007), Chairman of the Council of the European Synchrotron Radiation Facility (ESRF) (2006-2010), Chairmen of the European XFEL Council (2010-2014), Member of the Danish Academy of Technical Sciences (ATV) (since 2015), Chairman of the Board of MAX IV (since January 2023), member of the Board of Trustees of the Joachim Herz Foundation (since January 2023) and Member of the Scientific Advisory Board at the Advanced Light Source in Berkeley, USA (since 2024).

Read more on XFEL website

Image: The German Röntgen Museum honours Robert for his work on X-ray imaging methods.

Credit: European XFEL

Milestone for superconducting undulator

Milestone for superconducting undulator

A EUROPEAN XFEL TEAM AT THE KARLSRUHE INSTITUTE FOR TECHNOLOGY HAS TESTED A MOCK-UP COIL OF THE SUPERCONDUCTING UNDULATOR PRE-SERIES MODULE (S-PRESSO) DESIGNED FOR AN UPGRADE OF THE EUROPEAN XFEL. IT REACHED A WORLD RECORD MAGNETIC FIELD.

Undulators are one of the most important devices for a free-electron laser like the European XFEL in Schenefeld near Hamburg. With the help of a series of strong magnets an undulator creates an extremely brilliant light by forcing fast-moving electrons onto a slalom course. Furthermore, the undulators stimulate the electrons to emit laser-like electromagnetic radiation.

The strength of the magnets of an undulator determines the tunability of the photon energy range available for experiments. The Undulator Systems Group of European XFEL has started different activities in collaboration with Deutsches Elektronen-Synchrotron DESY to allow the implementation of superconducting undulators into the European XFEL in the upcoming years. The contract for superconducting undulator pre-series module (S-PRESSO) consisting of two pair of coils and a phase shifter has been assigned to Bilfinger Noell GmbH. Now, a European XFEL team at the Karlsruhe Institute for Technology has tested a 30-centimeter-long mock-up superconducting coil designed and build by Bilfinger Noell GmbH. The magnetic field of the S-PRESSO mock-up has reached 2 Tesla, which is larger ever reached before in such undulators.

Read more on the European XFEL website

Image: Undulators like this one cause highly accelerated electrons to emit intense and brilliant X-ray light. European XFEL is currently testing superconducting undulators in order to be able to offer users even better conditions for their research in the future.

European XFEL Young Scientist Award for Jiawei Yan

European XFEL Young Scientist Award for Jiawei Yan

Dr. Jiawei Yan was awarded the 2,000-euro prize for young scientists for the development of methods for generating ultrashort high-power pulses at the SASE2 line of the European XFEL.

He and a team from the FEL Physics group of the European XFEL and the MXL group at DESY, which is responsible for the operation of the XFEL, developed a method to achieve remarkably sharp current profiles with high peak currents.

Read more on XFEL website

Image: Marc Simon, Co-Chair of the User Organization Executive Committee, ceremonially presents the award to Jiawei Yan. 

Credit: European XFEL

Transition metal insulators: The origin of colour

Transition metal insulators: The origin of colour

In a theoretical study, researchers have explained the vibrant colours of two compounds whose electronic properties seemingly prohibit such colouring. The hues exhibited by the two insulators originate from transitions in the spins of the electrons, which modify the way the materials absorb and reflect light in such a way as to create the bright colours. The theoretical framework employed by the team promises new insights in fields such as optoelectronics or in the study of qubits, the quantum bits used in quantum computers. 

Although colour is a familiar phenomenon, it is sometimes challenging to explain how the hues of certain materials come about. This is the case with insulators that contain transition metals. In these compounds, the energy gap between the valence band, in which the electrons are tightly bound to the atoms, and the conduction band, in which the electrons can move freely, is larger than the highest energy of photons of visible light—meaning that these materials should not absorb visible light. As the colour of a compound is complementary to the wavelengths it absorbs, we should thus perceive these insulators as being transparent instead of coloured. 

A team of researchers including the head of the European XFEL Theory group, Alexander Lichtenstein, now used two complementary theoretical methods to study the origin of colour in two typical transition metal insulators: nickel(II) oxide (NiO)—a green compound used in the production of ceramics and nickel steel as well as in thin-film solar cells, nickel–iron batteries, and fuel cells—and manganese(II) fluoride (MnF2), a pink material employed in the manufacture of special kinds of glass and lasers.

Read more on XFEL website

Image: Visualization of the orbital character of low-laying excitons in NiO, corresponding to a local ‘Frenkel’ exciton at an energy of 1.6 eV and a weakly bound, bright ‘Wannier-Mottâ’ exciton at an energy of 3.6 eV

Milestone for novel atomic clock

Milestone for novel atomic clock

X-ray laser shows possible route to substantially increased precision time measurement

An international research team has taken a decisive step toward a new generation of atomic clocks. At the European XFEL X-ray laser, the researchers have created a much more precise pulse generator based on the element scandium, which enables an accuracy of one second in 300 billion years – that is about a thousand times more precise than the current standard atomic clock based on caesium. The team presents its success in the journal Nature.

Atomic clocks are currently the world’s most accurate timekeepers. These clocks have used electrons in the atomic shell of chemical elements, such as caesium, as a pulse generator in order to define the time. These electrons can be raised to a higher energy level with microwaves of a known frequency. In the process, they absorb the microwave radiation. An atomic clock shines microwaves at caesium atoms and regulates the frequency of the radiation such that the absorption of the microwaves is maximised; experts call this a resonance. The quartz oscillator that generates the microwaves can be kept so stable with the help of resonance that caesium clocks will be accurate to within one second within 300 million years.

Crucial to the accuracy of an atomic clock is the width of the resonance used. Current caesium atomic clocks already use a very narrow resonance; strontium atomic clocks achieve a higher accuracy with only one second in 15 billion years. Further improvement is practically impossible to achieve with this method of electron excitation. Therefore, teams around the world have been working for several years on the concept of a “nuclear” clock, which uses transitions in the atomic nucleus as the pulse generator rather than in the atomic shell. Nuclear resonances are much more acute than the resonances of electrons in the atomic shell, but also much harder to excite.

At the European XFEL the team could now excite a promising transition in the nucleus of the element scandium, which is readily available as a high-purity metal foil or as the compound scandium dioxide This resonance requires X-rays with an energy of 12.4 kiloelectronvolts (keV, which is about 10,000 times the energy of visible light) and has a width of only 1.4 femtoelectronvolts (feV). This is 1.4 quadrillionths of an electronvolt, which is only about one tenth of a trillionth of the excitation energy (10-19). This makes an accuracy of 1:10,000,000,000,000 possible. “This corresponds to one second in 300 billion years,” says DESY researcher Ralf Röhlsberger, who works at the Helmholtz Institute Jena, a joint facility of the GSI Helmholtz Centre for Heavy Ion Research, the Helmholtz Zentrum Dresden-Rossendorf (HZDR), and DESY.

Read more on the DESY website

Image: An artist’s rendition of the scandium nuclear clock: scientists used the X-ray pulses of the European XFEL to excite in the atomic nucleus of scandium the sort of processes that can generate a clock signal – at an unprecedented precision of one second in 300 billion years.

Credit: European XFEL/Helmholtz Institute Jena, Tobias Wüstefeld/Ralf Röhlsberger